Modern technology has produced a number of useful electronic identification methods and devices. Most familiar are the ubiquitous bar codes and magnetic strips that, together with their readers, are widely employed by businesses and others to perform several identification functions. The main reason bar codes and magnetic strips are so widely used is that they are very cheap.
Bar codes and magnetic strips are limited, however, by the relatively small amount of data they can encode and the effective range at which they can be read, which is quite short. Magnetic strips, for example, generally have such a limited range that the reader must be in direct contact with the strip in order to decode the data thereon. In the very few cases where a magnetic strip is read with a device other than a direct contact reader, the effective reading range is still only a few centimeters at best. Similarly, the effective range at which bar codes can be reliably read is typically no better than a few centimeters.
In addition to range limitations, both bar codes and magnetic strips are impossible to read if there is any obstruction between the reading device and the bar code or magnetic strip. When reading a magnetic strip or bar code, the orientation of the reading device relative to the bar code or magnetic strip also presents a problem. If the reading device is not properly aligned or is held at an incorrect angle, the encoded information can not be read. As a result of these problems, each individual read operation requires manual scanning by a human operator if high read accuracy is needed. The attractive feature of bar codes and magnetic strips is that they are inexpensive. However, their inherent limitations have prevented their use in a wide range of applications for machine readable tags where highly reliable and totally automated reading is required for read ranges of up to several meters.
The radio frequency identification (“RFID”) tag is another prior art type of identification device. When interrogated, RFID tags reflect or retransmit a radio frequency signal to return an encoded identification number to the interrogator. A good example of RFID tags is their usage in the collection of highway and bridge tolls. An RFID tag is positioned on a user's vehicle to respond to an interrogation signal when the vehicle passes through a toll collection point. A reading device connected to a computer processes the tag identification number and uses the decoded information to charge a toll to the user by deducting the amount due from the user's credit card or other account.
Prior art RFID tag devices are of two basic types; those that contain a microchip and those that do not. There is a radical difference in cost and performance between these two types; to such an extent, in fact, that they rarely compete with one another as to the appropriate type of use. As a general rule, chip tags cost more but have a larger data capacity than chipless tags. Chip tags, for example, are usually not available below a unit cost of about one dollar each when ordered in a quantity of less than one million; whereas many chipless tags are projected to cost less than 20 cents each, even when manufactured in quantities of one hundred thousand.
Most RFID tags will have a longer reliable range than magnetic strips and bar codes. As a rule, RFID tags can be interrogated without having as significant line-of-sight and orientation problems as are evidenced by bar codes and magnetic strips. Although chip tags do have a longer range than magnetic strip and bar code systems, the range at which they can be reliably used is still a limiting factor.
Chip tags are by far the most popular. A chip tag consists of four elements or features: (1) a computer microchip; (2) circuits for converting radio signals to computer data signals and back to radio signals; (3) an antenna; and (4) a means for providing DC power to the chip circuitry. In low cost RFID chip tags, the first two features are often partially or totally integrated into a single microchip, which integration requires certain compromises in tag performance (read range, number of bits, etc.). This combination of features also leads to certain integrated circuit (IC) cost and/or design compromises to accommodate both digital and radio frequency circuitry on a single IC. The impact of these design compromises can be partially compensated for by use of low radio frequency (RF) operating frequencies that, in turn, lead to rather large and expensive antennas.
The most daunting problem with chip tags is the need for DC power for the chip circuitry. The combination of environmental issues coupled with severe constraints on cost, size and weight usually requires that the tag not have a battery or other on-board power source. The only generally useable solution is to obtain DC power by converting RF power received from the tag reader signal into DC power within the tag. Those skilled in the pertinent art term tags without a battery or other power source as “passive” tags, while those that contain a battery or other source are termed as “active” tags. The passive method of providing DC power to a chip tag requires a more efficient tag antenna (i.e., larger size and cost) and higher transmitted power levels from the reader. It also requires added components which will either add to the cost of the microchip or to the cost of the tag for the required extra electrical components in the tag, which will also result in an increased tag size. The most important limitation of passive powered chip tags, however, is the severe restriction on the read range of the tag because a signal that is sufficiently strong to power the tag only extends a short distance from the tag reader antenna. Thus, while chip tags have the dominate share of the RFID market, the high cost and limited read range combine to prevent chip tags from replacing either bar codes or magnetic strips in any significant manner.
“Chipless” RFID tags do not contain a microchip but, instead, rely on magnetic materials or transistorless thin film circuits to store data. A major advantage of chipless RFID tags is their relatively low cost. The disadvantages of chipless tags include that they are range limited (several centimeters at the most) and only contain limited amounts of information. The severity of these problems has prevented their market acceptance in spite of their low cost potential.
In the year 2000, the current global market for conventional RFID systems and services is in the order of 500 million U.S. dollars. This market is largely for chip tags that typically cost from about one dollar to tens of dollars each. While chipless tags are not selling well, they have generated great interest from a number of potential users because of their low cost potential. A huge gap exists in the automatic identification market between the very low cost bar codes and the higher performing RFID chip tags. The overall market is clamoring for a technical solution to fill that gap. The critical characteristics of the new automatic identification technology to fill this gap are: (1) a cost of between one cent and ten cents per tag when manufactured in high quantities; (2) reliable reading without the need for manual scanning by a human operator; (3) reliable reading without a line of sight between the tag and tag reader (i.e., reliable reading even if the tag is scratched, or covered with dirt, or on the wrong side of the package, etc.); (4) a reliable read range of at least one to two meters; and (5) a tag data capacity of roughly 100 bits. Such tags are of vital interest to postal authorities, airlines and airports, mass transit authorities, animal breeders, the livestock industry, delivery businesses, any business with significant supply chains, particularly those that maintain inventory or handle fast moving consumer goods, and so on. These are all applications where a high priced tag is not practicable, particularly where the tag is disposable or is going to be sold with the product.
Accordingly, what is needed in the art is a reliable, economically priced, small identification tag upon which can be encoded substantial identification data that can be read at an adequate range and can be used in a variety of environments and for a variety of applications.